(1) Field of the Invention
The present invention relates generally to a buoyant cable antenna system and, in a more particular preferred embodiment, to a buoyant cable antenna system with extended frequency range capability.
(2) Description of the Prior Art
Present buoyant cable antenna systems which serve as a towed platform by underwater vehicles such as submarines consist of a horizontal wire antenna element used for reception in the LF through VHF frequency band (10 kHz-130 kHz). The horizontal antenna element lies on the surface of the ocean and reception is limited by transmission line attenuation, amplifier gain and antenna characteristics. Sea water attenuation, antenna gain and frequency patterns limit the use of a horizontal antenna element. The waves may frequently wash over the cable thereby interrupting transmissions. This is especially likely to happen when the platform is being towed through the water. Moreover, this type of towed platform is quite limited in the types of antennas that can be utilized therewith. Other towed platforms could be used, but are not capable of being deployed and retrieved into a submerged vessel.
The buoyant cable antenna must be flexible because a submerged submarine preferably launches the cable antenna through a transfer mechanism which bends the cable through a six-inch radius. Because flexibility is required, buoyant cable antennas have employed the horizontal wire antenna element which receives signals from the fore and aft (front and back) direction relative to its deployment. The limited antenna gain pattern limits the reception capability of the buoyant cable antenna.
Various inventors have addressed similar problems related to buoyant cable antennas as discussed in the following patents. Thus, the present invention addresses a long felt need for an improved buoyant cable antenna system.
U.S. Pat. No. 5,272,486, issued Dec. 21, 1993, to Stuart C. Dickinson, discloses an apparatus for erecting and stowing a communications antenna from an underwater buoyant cable. In its stowed position, the antenna is approximately parallel to the cable. In its erected position, the antenna is approximately perpendicular to the cable. A hinge, spring biased to maintain the antenna in its stowed position, is connected to the cable and to one end of the antenna. A shape memory alloy actuator is connected to the cable and the antenna. The actuator overcomes the spring bias of the hinge to raise the antenna to its erected position when energy of activation is supplied thereto. Further, the actuator allows the spring bias of the hinge to return the antenna to its stowed position when the energy of activation is removed there from.
U.S. Pat. No. 5,517,202, issued May 14, 1996, to Patel et al., discloses a buoyant antenna for providing sufficient transmission time windows for communication at ultra-high and extremely-high frequencies. The antenna is configured to float on the surface of a body of water and is connected to a vessel through a communications cable. The buoyant antenna has a length and a stabile or rotation resistant cross-section which minimizes wash over when deployed in a manner which essentially eliminates in line tension on the antenna. The antenna is cylindrically shaped with sensor elements offset from the centerline. A high density mass is placed diametrically opposite the sensor elements and a high buoyancy foam fills out the remaining cylindrical shape. The high density mass creates a righting moment to maintain the sensor elements above the water line. The absence of in line tension during communication periods serves also to eliminate any detectable wake during those communication periods. The lack of detectability makes the antenna and its deployment method particularly well suited for use when the vessel is a submarine.
U.S. Pat. No. 5,933,117, issued Aug. 3, 1999, to Erich Max Gerhard, discloses a buoyant loop antenna, deployable along a cable that includes a core region comprising a plurality of annular ferrite beads. These annular shaped beads include a center hole and generally concave first end and a generally convex second end. The ferrite beads are aligned with the concave end of one bead against the convex end of another bead. This allows the cable to flex while the beads maintain contact with each other, providing flexibility and resistance to crushing. The core region has a loop wire wrapped helically around it, forming the loop antenna. The loop wire element starts and ends at the same end of the core region, forming a loop. This loop allows transmission and reception in the athwart (side to side) direction. This novel wire loop antenna can be combined with a straight wire antenna (which provides reception in a fore and aft direction) to provide an omni-directional cable antenna assembly.
U.S. Pat. No. 3,961,589, issued Jun. 8, 1976, to Anthony Joseph Lombardi, discloses a reeling system that is contained within a buoy towed by a submerged submarine. The reeling system includes a pressure sealed housing, a cable reel disposed for rotation within the housing and a buoyant cable antenna disposed in an ejecting and retracting relationship with the reel. One end of the cable antenna extends from the housing to the exterior of the buoy. A cylinder-piston arrangement having a sea water inlet and a connection to the housing is responsive to the pressure of the sea water at the inlet to control air pressure in the housing to provide a pressure difference between the air pressure in the housing and the pressure of the sea water on the one end of the cable antenna exterior of the buoy for ejection and retraction of the cable antenna from and into the buoy.
U.S. Statutory Invention Registration No. H1220, published Aug. 3, 1993, to Brian L. Pease, discloses a VLF-VHF broadband in-line amplifier that forms a portion of a towable buoyant cable antenna system that is deployed in seawater from submarines. The amplifier is located between an antenna system and a coaxial cable. The coaxial cable is connected to the submarine. The VLF-VHF broadband in-line amplifier provides substantially uniform amplification for the frequency range of 10 kHz-160 MHz on signals received from the antenna system. The amplified signals are then transmitted to the submarine over the coaxial cable.
The above patents do not describe a platform that can utilize a wide range of antennas, maintain the antenna far enough above the surface of the water to prevent washover communication breakdown, and, if desired, operate while a submarine is moving. The solutions to the above-described problems have been long sought without success. Consequently, those skilled in the art will appreciate the present invention that addresses the above and other problems.